chore: update readme

README.md

@@ -29,10 +29,16 @@ docker compose up -d
 Please only use this platform setup for testing purposes.
 
 ### Deployment
-Before deploying the gateway via docker containers, the environment variables need to be configured in `.env` data.
-This can be created from a copy of the `env.EXAMPLE`.
+Before deploying the gateway via docker containers, the environment variables need to be configured in `.env` in the root directory.
+This can be created from the provided `env.EXAMPLE`.
 The default values can be directly used for the test deployment.
-Check [here](https://github.com/N5GEH/n5geh.tools.mqtt-gateway#environment-variables) for more information about the environment variables
+Check [here](https://github.com/N5GEH/n5geh.tools.mqtt-gateway#environment-variables) for more information about the environment variables. 
+
+There are two methods to deploy the gateway: 1) pull images from GitHub Container Registry, or 2) building your local images.
+
+> **Important**: The frontend can currently only be built locally, because of the limitation of the used framework.
+> Therefore, `VITE_API_URL` has to be set up in `./frontend/.env` as shown in `./frontend/.env.example`.
+> `VITE_API_URL` refers to the URL to access the Gateway api from the client side (i.e., your browser)
 
 #### Pull docker images
 The recommended way to deploy the MQTT gateway is to use the pre-built docker images. Under the packages of this repository, you can find the images for the `gateway`, `frontend`, and `API`. In oder to pull these images, you need to first sign in to the `ghcr.io` (GitHub Container Registry).